全文获取类型
收费全文 | 1490篇 |
免费 | 8篇 |
国内免费 | 43篇 |
专业分类
安全科学 | 49篇 |
废物处理 | 93篇 |
环保管理 | 146篇 |
综合类 | 252篇 |
基础理论 | 344篇 |
环境理论 | 1篇 |
污染及防治 | 420篇 |
评价与监测 | 112篇 |
社会与环境 | 118篇 |
灾害及防治 | 6篇 |
出版年
2023年 | 13篇 |
2022年 | 48篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 15篇 |
2018年 | 54篇 |
2017年 | 25篇 |
2016年 | 31篇 |
2015年 | 52篇 |
2014年 | 39篇 |
2013年 | 126篇 |
2012年 | 37篇 |
2011年 | 71篇 |
2010年 | 64篇 |
2009年 | 73篇 |
2008年 | 72篇 |
2007年 | 63篇 |
2006年 | 45篇 |
2005年 | 48篇 |
2004年 | 83篇 |
2003年 | 71篇 |
2002年 | 45篇 |
2001年 | 105篇 |
2000年 | 43篇 |
1999年 | 24篇 |
1998年 | 17篇 |
1997年 | 12篇 |
1996年 | 9篇 |
1995年 | 22篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1980年 | 6篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1972年 | 12篇 |
1971年 | 5篇 |
1966年 | 5篇 |
1965年 | 5篇 |
1959年 | 5篇 |
1957年 | 5篇 |
排序方式: 共有1541条查询结果,搜索用时 640 毫秒
371.
372.
Chorionic villus sampling (CVS) was performed in 12 pregnant women (9–25 gestational weeks) with ultrasonographic evidence of missed abortion. An ultrasonographically guided transabdominal (eight cases) or transcervical (four cases) approach was used. Fetal karyo-typing was successful in all cases; in five, chromosomal aberrations were found and in seven, chromosome analyses revealed normal karyotypes. Tissue culture for fetal karyotyping was successful in only 72.5 per cent of 40 live pregnancies which were electively interrupted because of abnormal ultrasonographic findings or an abnormal fetal karyotype, and in 57 per cent of seven missed abortions. CVS is suggested as a feasible and effective method for fetal karyotyping in missed abortions and it seems to be superior to post-abortion tissue culture. 相似文献
373.
Nine patients with oligohydramnios and amnio-chorionic separation were identified out of 7000 women who underwent a vaginal ultrasound examination at 15–16 weeks' gestation. Oligohydramnios was defined as a reduced amount of amniotic fluid, a distance of more than 1 cm between the chorion and amnion, and a good turgor of the amnion without floating membranes or intrauterine sheets. Fetal malformations were observed in all nine cases. In four of six fetuses where chromosomal analysis was available, an abnormal karyotype was found. It is concluded that oligohydramnios in the early second trimester is associated with fetal abnormality. 相似文献
374.
A twin pregnancy with one hydrocephalic fetus with oligohydramnios is presented. Sonographic evaluation could not exclude monochorionicity. Before considering selective feticide, blood samples from both fetuses were examined for DNA ‘fingerprint’ analysis. The different banding patterns of the blood samples established dizygosity. This procedure is suggested in cases where sonography fails to determine chorionicity. 相似文献
375.
Encephalocele is the most common cause of occipital midline extracranial mass associated with hydrocephalus. A case is presented where an occipital extracranial mass associated with hydrocephalus which was detected on second-trimester ultrasound examination turned out to be a haemangioma, a relatively benign lesion. We suggest that haemangioma should be considered in the differential diagnosis of extracranial masses detected prenatally. 相似文献
376.
Model calculating annual mean atmospheric dispersion factor for coastal site of nuclear power plant 总被引:1,自引:0,他引:1
HU Er-bang YAO Ren-tai ZHANG Mao-shuan GAO Zhan-rong WANG Shu-xian CHEN Jia-yi JIA Pei-rong Liao Qi-lin 《环境科学学报(英文版)》2001,13(3):280-290
IntroductionAnatmospheredispersionfieldexperimentwasdoneonthecoastalsiteofnuclearpowerplant (NPP)intheeastpartofChinaduring 1995— 1996 Thecontentofthisexperimentincludes:hourlyobservationofwindandtemperatureonthetowerof10 0m ;Observationofsurfacewindandseeandl… 相似文献
377.
378.
Dense nonaqueous phase liquids (DNAPLs) are immiscible with water and can give rise to highly fingered fluid distributions when infiltrating through water-saturated porous media. In this paper, a conceptual mobile–immobile–zone (MIZ) model is presented to describe the structure of a DNAPL finger in water-saturated porous media and the velocity of finger propagation. A finger is composed of a finger body and a tip. The finger body has a mobile core and an immobile sheath. All the DNAPL within the tip of a finger is mobile. Lab experiments utilizing image analyses of a DNAPL (PCE) penetrating into water-saturated homogeneous glass beads were carried out in a two-dimensional transparent chamber. The results show that the fingers elongated almost linearly with time. The fingers did not grow laterally after the tip of the finger had passed. The average finger diameters were between 3.9 and 5.4 mm for PCE propagation in water-saturated glass bead porous media with mean particle diameters from 0.32 to 1.36 mm. The estimated mobile core diameters were 51–60% of the average finger diameters. 相似文献
379.
In this study, spatial and temporal distributions of three gelatinous macrozooplankton, the scyphozoan Aurelia aurita and the ctenophores Pleurobrachia pileus and Mnemiopsis leidyi, were evaluated using the data obtained from seven southern Black Sea cruises carried out from 1996 to 1999. A comparison of nets used for the sampling of gelatinous macrozooplankton illustrated the superiority of the Hensen net with a larger mesh size (300 µm) over the Nansen net (112 µm). P. pileus was mainly concentrated below the mixed layer, while A. aurita and M. leidyi were generally confined to surface waters. Horizontally, P. pileus was associated with deep, offshore waters. P. pileus also displayed the least interannual variation of the three species. Biomass of A. aurita and M. leidyi varied substantially seasonally and inter-annually. In September 1999, the average biomass of M. leidyi was at its lowest level (12 g wet weight m-2) since its explosive development at the end of the 1980s. This was associated with the appearance of the new predatory ctenophore Beroe ovata, which appeared in the Black Sea at the end of the 1990s. 相似文献
380.
Emergy evaluation and economic analysis of three wetland fish farming systems in Nansi Lake area,China 总被引:2,自引:0,他引:2
Emergy and economic methods were used to evaluate and compare three fish production models, i.e., cage fish farming system, pond intensive fish rearing system and semi-natural extensive pond fish rearing system, in Nansi Lake area in China in the year 2007. The goal of this study was to understand the benefits and driving forces of selected fish production models from ecological and economic points of view. The study considered input structure, production efficiency, environmental impacts, economic viability and sustainability. Results show that the main difference among the three production systems was the emergy cost for fish feed associated with their feeding system, i.e., feeding on natural biomass such as plankton and grass or on commercial feedstock. As indicated by EYR, ELR and ESI, it can be clearly shown that the intensive production model with commercial feed is not a sustainable pattern. However, the point is that more environmentally sound patterns do not seem able to provide a competitive net profit in the short run. The intensive pond fish farming system had a net profit of 2.57E+03 $/ha, much higher than 1.27E+03 $/ha for cage fish farming system and slightly higher than 2.37E+03 $/ha for semi-natural fish farming system. With regard to the drivers of local farmer’s decisions, the accessibility of land for the required use and investment ability determine the farmer’s choice of the production model and the scale of operation, while other factors seem to have little effect. Theoretically, the development of environmentally sustainable production patterns, namely water and land conservation measures, greener feed as well as low waste systems is urgently needed, to keep production activities within the carrying capacity of ecosystems. Coupled emergy and economic analyses can provide better insight into the environmental and economic benefits of fish production systems and help solve the problems encountered during policy making. 相似文献